Binding agents for radiation-cured aqueous paints

ABSTRACT

The invention relates to binding agents for radiation-cured aqueous paints, said agents containing reaction products ABCDE composed of A epoxy compounds with at least two epoxy groups per molecule, B unsaturated fatty acids, C olefinically unsaturated monomers, D compounds containing unsaturated aliphatic hydroxyl groups and E multi-functional isocyanates, whereby the compounds C are always directly bonded to the compounds B, the compounds D are always directly bonded to the compounds E and the compounds A are always directly bonded to the compounds B. The invention also relates to methods for producing said binding agents and to the use thereof.

FIELD OF THE INVENTION

The invention relates to binders for radiation-curable water-basedpaints.

BACKGROUND OF THE INVENTION

Water-based paints curable by irradiation with UV light are known fromEP-B 0 694 531 and AT-B 404 733. They contain water-dilutable urethaneresins as binders.

However, these paints have disadvantages in practical use. Inparticular, they do not meet the corrosion protection requirements forthe painting of metals.

The object is therefore to provide water-dilutable binders for thepainting of metals, especially base metals, which give good corrosionprotection, where curing may be effected by irradiation with high-energylight.

It has been found that radiation-curable water-dilutable paints based onbinders derived from epoxy resins provide coatings with good corrosionprotection.

The present invention therefore relates to binders for radiation-curablewater-based paints, comprising reaction products ABCDE of epoxycompounds A having at least two epoxide groups per molecule, unsaturatedfatty acids B, olefinically unsaturated monomers C, unsaturatedaliphatic compounds containing hydroxyl groups, D, and polyfunctionalisocyanates E. The compounds C are always directly bonded to thecompounds B; likewise, the compounds D are always directly bonded to thecompounds E, and the compounds A are always directly bonded to thecompounds B.

The invention also provides a process for the preparation of the bindersaccording to the invention.

Finally, the invention further relates to mixtures of the bindersaccording to the invention with aqueous dispersions of acrylatecopolymers.

The epoxy compounds A have at least two epoxide groups per molecule andcan be aliphatic, aromatic or mixed aromatic-aliphatic. Suitablealiphatic diepoxides or polyepoxides are especially alpha,omega-diepoxyalkanes, such as 1,5-diepoxyhexane or 1,7-diepoxyoctane,ethers of glycidyl alcohol with dihydric or more than dihydric alcoholshaving from 2 to 20 carbon atoms, such as butanediol diglycidyl ether orhexanediol diglycidyl ether and trimethylolpropane triglycidyl ether,ethers of glycidyl alcohol with polyethylene or polypropylene glycol, oresters of glycidyl alcohol with dibasic or more than dibasic aliphaticcarboxylic acids, such as diglycidyl adipate, diglycidylhexahydrophthalate or diglycidyl esters of dimeric fatty acids. Suitablearomatic diepoxides or polyepoxides are diepoxydivinylbenzene anddiepoxydivinylnaphthalene. Suitable mixed aromatic-aliphatic diepoxidesor polyepoxides are the diglycidyl ethers of bisphenol A, bisphenol F,dihydroxybiphenyl or dihydroxydiphenyl sulfone. Other suitable compoundsare addition products of the said diepoxides or polyepoxides withdifunctional or more than difunctional hydroxyl compounds, for examplethe bisphenol A-based epoxy resins obtained by an advancement reaction.

The unsaturated fatty acids B are linear or branched aliphaticmonocarboxylic acids and have at least one olefinic double bond and from6 to 30 carbon atoms. Suitable compounds are, inter alia, palmitoleicacid, oleic acid, elaidic acid, linoleic acid, linolenic acid,elaeostearic acid, arachidonic acid, erucic acid and clupanodonic acid,as well as mixtures thereof, especially the technical-grade mixturesobtained by the saponification of oils.

Particularly preferred compounds are fatty acids and mixtures thereofwhich have at least two olefinic double bonds, which in turn arepreferably non-conjugated. Linseed oil fatty acid, tall oil fatty acidand sunflower oil fatty acid are particularly suitable.

The olefinically unsaturated monomers C contain a mass fraction of atleast 10% of an olefinically unsaturated acid, preferably anolefinically unsaturated carboxylic acid or dicarboxylic acid. It isalso possible to use half-esters of olefinically unsaturateddicarboxylic acids with one mol of an alcohol per one mol of adicarboxylic acid. Preferred olefinically unsaturated acids are acrylicand methacrylic acid, vinylacetic acid and crotonic and isocrotonicacid. Examples of half-esters which can preferably be used are themonomethyl esters of maleic acid, fumaric acid, itaconic acid,citraconic acid or mesaconic acid. Esters of the said acids withmonohydric or polyhydric alcohols, such as methyl (meth)acrylate, ethyl(meth)acrylate, n-propyl or isopropyl (meth)acrylate, n-butyl ortert-butyl (meth)acrylate or 2-ethylhexyl (meth)acrylate, as well asdiesters of the said dicarboxylic acids, such as dimethyl maleate, andhydroxy-functional compounds (also used as compounds D), such ashydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl(meth)acrylate and trimethylolpropane mono(meth)acrylate ordi(meth)acrylate, can be used in a mixture with the said acidicmonomers. Other suitable monomers are styrene, vinyltoluene,alpha-methylstyrene, para-methylstyrene, vinyl acetate and(meth)acrylonitrile.

The unsaturated aliphatic compounds containing hydroxyl groups, D, areesters of dihydric or more than dihydric alcohols with monomerscontaining olefinically unsaturated acid groups, especially with acrylicand methacrylic acid. Hydroxyethyl and hydroxypropyl (meth)acrylate areparticularly suitable.

The polyfunctional isocyanates E are aromatic, aliphatic and mixedaromatic-aliphatic isocyanates having at least two isocyanate groups.Preference is given to aliphatic isocyanates and those aromaticisocyanates, including diisocyanates, in which the isocyanate groups arebonded to an aliphatic carbon atom, such as xylylene diisocyanate andtetramethylxylylene diisocyanate. Preferred aliphatic isocyanates arelinear, branched and cyclic isocyanates having from 4 to 12 carbonatoms, such as hexamethylene diisocyanate, trimethylhexane diisocyanate,isophorone diisocyanate and 1,3- and 1,4-bis(isocyanato)cyclohexane.

The invention further relates to a process for the preparation of thebinders ABCDE, wherein, in the first step, the epoxy compounds A arereacted with the unsaturated fatty acids B to give adducts, the amountsof the educts being chosen so that there is at least 0.5 mol of acidgroups in the fatty acids B per one mol of epoxide groups in A. A ratioof at least 0.7 mol/mol, especially from 0.9 mol/mol to 1.0 mol/mol, ispreferred. In the second step, the adducts AB formed in this way arereacted with the olefinically unsaturated monomers C in the presence offree radical initiators, the compounds C polymerising and at leastpartially forming grafts on the adducts AB, and the grafting preferablytaking place at the double bonds of the fatty acids. The graftcopolymers ABC formed in the second step are then reacted with thesemicapped isocyanates DE, prepared in a separate step by reacting thehydroxy-functional, olefinically unsaturated monomers D with thepolyfunctional, preferably difunctional, isocyanates E, to give theproducts ABCDE by urethane formation. The reaction is preferably carriedout in such a way that the ratio of the amount of substance isocyanategroups in DE to the amount of substance hydroxyl groups in B is 0.2 to0.9, the ratio preferably being chosen so that the reaction productABCDE has an acid number of 5 mg/g to 80 mg/g, especially of 10 mg/g to50 mg/g.

The acid number is defined according to DIN EN ISO 3682 as the ratio ofthe mass of potassium hydroxide, mKOH, required to neutralise a testsample, to the mass of this sample, M_(B) (mass of the solid in thesample in the case of solutions or dispersions); its conventional unitis “mg/g”.

The binders according to the invention are particularly suitable for theformulation of radiation-curable coating agents (curable by UV radiationor electron beams). Photoinitiators are added; on irradiation withhigh-energy light, these form radicals which initiate curing bypolymerisation. A particular feature of the binders according to theinvention is their good compatibility with aqueous acrylate dispersions.Such dispersions can be admixed in a mass ratio of up to 50:50 (based ineach case on the mass of solids in the dispersions) without adverselyaffecting the curing rate or the properties of the resulting coatingfilm. The known acrylate dispersions containing hydroxyl groups, as wellas self-crosslinking acrylate dispersions, are suitable here.

Preferred acrylate dispersions are self-crosslinking acrylatedispersions based on copolymers of (meth)acrylic acid esters of linearor branched aliphatic monoalcohols having 3 to 10 carbon atoms,(meth)acrylic acid esters of methanol and ethanol, (meth)acrylic acidesters of dihydric aliphatic alcohols having 2 to 6 carbon atoms,especially glycol, 1,2- and 1,3-propanediol, 1,2- and 1,4-butanediol and1,6-hexanediol, styrene and vinyltoluene, as well as olefinicallyunsaturated monomers containing carbonyl groups, such as diacetoneacrylamide, and hydroxy-functional acrylate dispersions based oncopolymers of (meth)acrylic acid esters of linear or branched aliphaticmonoalcohols having from 3 to 10 carbon atoms, (meth)acrylic acid estersof methanol and ethanol, (meth)acrylic acid esters of dihydric aliphaticalcohols having from 2 to 6 carbon atoms, especially glycol, 1,2- and1,3-propanediol, 1,2- and 1,4-butanediol and 1,6-hexanediol, styrene andvinyltoluene. In the case of the self-crosslinking acrylate dispersions,diamines or, preferably, dihydrazines or dihydrazides of aliphaticdicarboxylic acids having from 2 to 8 carbon atoms are used; adipic aciddihydrazide is particularly preferred.

The binders formulated in this way can be used to produce coatings evenon base metals, imparting good corrosion protection to the substrate.

The invention is illustrated by the Examples below.

EXAMPLES Example 1

560 g of linseed oil fatty acid were heated to 140° C. with 0.6 g oftriphenylphosphine as catalyst. 380 g of bisphenol A diglycidyl etherwere added over two hours, with thorough stirring, and the mixture wasstirred at this temperature until epoxide groups were no longerdetectable.

Example 2

100 g of the fatty acid epoxy adduct of Example 1 were heated to 140° C.with 70 g of xylene. A mixture of 29.0 g of butyl methacrylate and 15.6g of methacrylic acid and, separately therefrom, 2.0 g of ditert.-butylperoxide were added to the previous mixture over 8 hours. When theaddition had ended, the resulting mixture was kept at 140° C. for afurther 2 hours and then cooled to room temperature. The mass fractionof solids of the resulting solution was 68.1%.

Example 3

222.3 g of isophorone diisocyanate were heated to 50° C. with 0.5 g oftriphenyl phosphite. 116.1 g of hydroxyethyl acrylate and 0.2 g ofhydroquinone monomethyl ether were added over one hour and the mixturewas then heated to 80° C., with stirring, and kept at this temperatureuntil the mass fraction of free isocyanate groups had dropped to 12%.

Example 4

140 g of the product of Example 2 were mixed with 40.0 g of the productof Example 3 and stirred at 80° C. until the proportion by mass of freeisocyanate groups had dropped below 0.1%. The temperature was thenraised to 130° C. and the xylene was stripped off by distillation underreduced pressure. After cooling to 95° C., 28 g of an aqueous solutionof lithium hydroxide (5 g of LiOH in 100 g of aqueous solution) wereadded. 146 g of demineralised water were then added over one hour at 95°C. to give an aqueous dispersion with a mass fraction of solids ofapprox. 44% and an acid number of 47.8 mg/g.

Example 5

222.3 g of isophorone diisocyanate were heated to 40° C. with 0.25 g ofdibutyltin dilaurate and 0.5 g of triphenyl phosphite. 130.1 g ofhydroxypropyl acrylate and 0.2 g of hydroquinone monomethyl ether wereadded over one hour and the mixture was then heated to 80° C., withstirring, and kept at this temperature until the mass fraction of freeisocyanate groups had dropped to 12%.

Example 6

60.0 g of the product of Example 5, 0.01 g of dibutyltin dilaurate and0.5 g of hydroquinone monomethyl ether were admixed at 80° C. to 147.1 gof the product of Example 2 and the mixture was stirred at 80° C. untilthe mass fraction of free isocyanate groups had dropped below 0.1%. Thetemperature was then raised to 130° C. and the xylene was stripped offby distillation under reduced pressure. After cooling to 95° C., 29.1 gof an aqueous solution of lithium hydroxide (5 g of LiOH in 100 g ofaqueous solution) were added. 215 g of demineralised water were thenadded over one hour at 95° C. to give an aqueous dispersion with a massfraction of solids of approx. 40%.

Example 7 Paint Test

100 g of each of the products of Example 4 and Example 6 were processedto the paints 7.1 and 7.2 with the addition of 6 g of a solution ofIrgacure 184 in butyl glycol (50 g of ®Irgacure 184 in 100 g ofsolution).

The following results were obtained:

After application of the paints to an iron sheet with a wet filmthickness of 120 μm, drying at from 50° to 60° C. for 10 minutes andthen curing by irradiation with a mercury vapour lamp (power: 80 W, at adistance of 10 cm and with a conveyor belt speed of 4 m/min), a smoothspeck-free coating was obtained. The measured Erichsen cupping (ISO1520) was 9 mm in both cases and the results of the impact test(Erichsen, ASTM D 2794-90) and crosshatch test (DIN EN ISO 2409) were10/10 and 3/5 for the paint 7.1 and 30/20 and 0/5 for the paint 7.2.

Example 8 Resistance Test on Wood

After application of the said paints of Example 7 to wooden boards (200μm, two coats with drying at from 50° C. to 60° C. for 10 minutes aftereach coat) and curing as in Example 7, the resistance of the coatingswas measured according to DIN 68861, Part 1A. The following results wereobtained (exposure time of 16 hours in each case): Coating with Coatingwith Test material paint 7.1 paint 7.2 Aqueous ammonia solution (10%) 00 Aqueous ethanol solution (48%) 0 0 Red wine 0 0 Coffee powder 0 1Black tea 0 0 Demineralised water 0 0 Lipstick 0 0 Black ballpoint penink 0 0

Example 9 Mixtures With Acrylate Dispersions

Mixtures of the paints 7.1 and 7.2 with various acrylate dispersionswere prepared:

-   -   9.1 self-crosslinking acrylate dispersion based on butyl        acrylate/methyl methacrylate/diacetone acrylamide copolymer and        adipic acid dihydrazide as crosslinking agent; mass fraction of        solids: 45%    -   9.2 hydroxy-functional acrylate dispersion based on butyl        acrylate, butyl methacrylate and styrene    -   9.3 hydroxy-functional acrylate dispersion based on butyl        methacrylate, hydroxyethyl methacrylate and styrene    -   9.4 self-crosslinking acrylate dispersion based on        butyl-acrylate/methyl-methacrylate/styrene/diacetone-acrylamide        copolymer and adipic acid dihydrazide as crosslinking agent

The mixtures (ratio of the mass of solids in the binder according to theinvention relative to that of acrylate: 90:10, 75:25 and 50:50) areclear (without turbidity) in all cases and the coated surfaces arefaultless without exception when using the paint 7.1, whereas a fewstreaks could be observed on the surface when using the paint 7.2 withthe acrylate dispersion 9.3. When mixing commercial radiation-curablebinders with acrylate dispersions in accordance with those mentionedabove, turbidity was observed in the mixture in all cases; all thesurfaces coated therewith exhibited imperfections in the film.

1. Binders for radiation-curable water-based paints, comprising reactionproducts ABCDE of epoxy compounds A having at least two epoxide groupsper molecule, unsaturated fatty acids B, olefinically unsaturatedmonomers C, unsaturated aliphatic compounds containing hydroxyl groups,D, and polyfunctional isocyanates E, characterised in that the compoundsA are bonded to the compounds B by a beta-hydroxyester bond and thecompounds C at least partially form grafts on the adducts AB to givecompounds ABC, in that the compounds D are bonded to the compounds E bya urethane group to give semicapped isocyanates DE, and in that thecompounds ABC are bonded to the compounds DE, likewise with urethaneformation.
 2. Binders according to claim 1, characterised in that theepoxy compounds A are selected from the group consisting of ethers ofglycidyl alcohol with dihydric or more than dihydric alcohols havingfrom 2 to 20 carbon atoms, ethers of glycidyl alcohol with polyethyleneor polypropylene glycol, esters of glycidyl alcohol with dibasic or morethan dibasic aliphatic carboxylic acids, and diglycidyl ethers ofbisphenol A, bisphenol F, dihydroxybiphenyl and dihydroxydiphenylsulfone, and addition products of the said diepoxides with difunctionalor more than difunctional hydroxyl compounds.
 3. Binders according toclaim 1, characterised in that the unsaturated fatty acids B are linearor branched aliphatic monocarboxylic acids and have at least oneolefinic double bond and from 6 to 30 carbon atoms.
 4. Binders accordingto claim 1, characterised in that the olefinically unsaturated monomersC contain a mass fraction of at least 10% of an olefinically unsaturatedacid.
 5. Binders according to claim 1, characterised in that theunsaturated aliphatic compounds containing hydroxyl groups, D, areesters of dihydric or more than dihydric alcohols with monomerscontaining olefinically unsaturated acid groups.
 6. Binders according toclaim 1, characterised in that the polyfunctional isocyanates E arearomatic, aliphatic and mixed aromatic-aliphatic isocyanates having atleast two isocyanate groups.
 7. A process for the preparation of bindersaccording to claim 1, characterised in that in the first step, the epoxycompounds A are reacted with the unsaturated fatty acids B to giveadducts, at least 0.5 mol of acid groups in the fatty acids B being usedper 1 mol of epoxide groups in A, in the second step, the adducts ABformed in this way are reacted with the olefinically unsaturatedmonomers C in the presence of free radical initiators, the compounds Cpolymerising and at least partially forming grafts on the adducts AB, ina separate third step, semicapped isocyanates DE are prepared byreacting the hydroxy-functional, olefinically unsaturated monomers Dwith the poly-functional, preferably difunctional, isocyanates E, and inthe fourth step, the isocyanates DE are reacted with the graftcopolymers ABC formed in the second step to give the products ABCDE byurethane formation.
 8. The process according to claim 7, characterisedin that a ratio of at least 0.7 mol/mol is chosen in the first step. 9.The process according to claim 7, characterised in that a ratio of theamount of substance of isocyanate groups in DE to the amount ofsubstance of hydroxyl groups in B of 0.2 to 0.9 is chosen in the fourthstep.
 10. The process according to claim 7, characterised in that theratio of the amounts of substance in the fourth step is chosen so thatthe reaction product ABCDE has an acid number of from 5 mg/g to 80 mg/g.11. A method of use of binders according to claim 1 for the preparationof radiation-curable coating agents for wood, metal and plastics,comprising mixing the binders according to claim 1 and photoinitiators.12. The method of use according to claim 11, comprising admixing aqueousacrylate dispersions.